Polymer electrolyte membranes are useful in electrochemical devices such as batteries and fuel cells since they function as electrolyte and separator. Such membranes may be readily fabricated as thin flexible films which can be incorporated into cells of variable shape.
Perfluorinated hydrocarbon sulfonate ionomers, such as Nafion® by DuPont or analogous Dow perfluorinated polymers, are presently used as polymer electrolyte membranes for fuel cells. Such prior art membranes, however, have severe limitations when used in hydrogen/air fuel cells and liquid feed direct methanol fuel cells.
Perfluorinated hydrocarbon sulfonate ionomer membranes cannot be operated over a prolonged period of time at temperatures higher than 85° C. without showing decomposition and performance degradation. As such, they cannot be used in hydrogen/air fuel cells at 120° C. or higher as required to minimize poisoning of the anode catalyst by carbon monoxide which is present when reformate hydrogen gas is used.
Perfluorinated hydrocarbon sulfonate ionomer membranes have also been shown to have high permeability to liquid methanol. Therefore, liquid feed direct methanol polymer electrolyte membrane fuel cells based on Nafion® or similar perfluorinated hydrocarbon sulfonate ionomer membranes have poor efficiency and low power densities.
Accordingly, it is an object herein to provide polymer membranes which have high proton conductivity, high temperature stability and/or low methanol permeability.